Resuscitators

ABSTRACT

A gas-powered resuscitator is operable either in a manual mode or an automatic mode. The resuscitator includes an oscillatory timing valve ( 14 ) having an outlet ( 23 ) connected to a bi-stable valve ( 25 ), the operation of which is piloted by a manual valve ( 16 ). The outlet ( 26 ) of the bi-stable valve ( 25 ) connects to the outlet ( 2 ) of the resuscitator via a rotatable control ( 32 ) and a patient valve ( 41 ). The outlet ( 26 ) of the bi-stable valve ( 25 ) also connects to the control inlet ( 34 ) of the timing valve ( 14 ). The manual valve ( 16 ) has a button ( 62 ) that can be pushed down manually in the manual mode or can be held down in the automatic mode by rotating a locking ring ( 262 ). The maximum duration of cycles is limited by operation of the timing valve ( 14 ), whether the resuscitator is operated manually or automatically.

This invention relates to resuscitators of the kind operable in a first,automatic mode whereby gas is delivered to a patient in a regulatedcyclical fashion repeatedly until the mode is terminated and in a secondmode whereby a cycle of gas is delivered in response to actuation of amanual member.

Resuscitators are used to supply breathing gas to a patient who may notbe breathing spontaneously. Portable resuscitators may take the form ofa resilient bag that is squeezed manually to supply a volume of air tothe patient, the bag refilling with air when it is released so that anew volume of air can be supplied. Alternatively, the resuscitator maybe a mechanical device including a tiring valve and various othercontrols and is connected to an oxygen cylinder, which both provides thebreathing gas, or a part of this, and which may also provide the powerto drive the components of the resuscitator. Examples of suchresuscitators are described in GB 2174760, GB 2174609, EP 343818, EP342883, EP 343824, GB 2282542, EP 691137, GB 2284159 and GB 2270629.These resuscitators are arranged to supply gas in a cyclic manner to thepatient at a rate compatible with normal breathing. The resuscitatorusually has some form of manual override so that gas can be provided ata selectively controllable rate such as when the patient is receivingCPR. Existing resuscitators suffer from various problems. For example,where the resuscitator can be operated fully manually, there is a riskthat an inexperienced operator could provide inappropriate rates ofbreathing with possible danger to the patient. Other resuscitators donot allow sufficient flexibility in the administration of gas.

It is an object of the present invention to provide an alternativeresuscitator.

According to one aspect of the present invention there is provided aresuscitator of the above-specified kind, characterised in that theresuscitator is arranged such that the cycle is only delivered for solong as the manual member is actuated and that the resuscitator controlsthe maximum length of the cycle.

The resuscitator may be arranged to deliver repeated ventilation cycleswhile the manual member is actuated and the resuscitator preferablyincludes a locking device for holding the manual member in an actuatedposition. The manual member may include a button that is depressed toactuate a gas delivery cycle, the locking device including a rotatablemember operable to retain the button in an actuated position. Therotatable member may extend around the button and be arranged to depressthe button when rotated. The rotatable member and the button preferablyhave cooperating cam formations. The resuscitator preferably includes afirst valve controlled by operation of the manual member and a bi-stablevalve connected with the first valve to be operated between a fully openor a fully closed position by an output from the first valve, thebi-stable valve controlling supply of gas to the outlet of theresuscitator. The resuscitator preferably includes a timing valveoperable to supply cycles of ventilation gas to a patient valveassembly, the output of the timing valve being connected to a manualvalve assembly operable by the manual member to prevent or enable flowof ventilation gas to the patient valve assembly, and the output of themanual valve assembly being connected to a control inlet of the timingvalve. The resuscitator may include a manually-displaceable controlmember that is displaceable to alter timing frequency and flow ratesimultaneously. The resuscitator may include a gas entrainment device,the manually-displaceable control member being operable alsosimultaneously to control supply of entrainment gas to the entrainmentdevice. The manually-displaceable control member preferably includes arotatable member.

According to another aspect of the present invention there is provided aresuscitator including a timing valve operable to supply cycles ofventilation gas to a patient valve assembly, characterised in that theoutput of the timing valve is connected to a manual valve assembly,which is operable to prevent or enable flow of ventilation gas to thepatient valve assembly, and that the outlet of the manual valve assemblyis connected to a control inlet of the timing valve.

According to a further aspect of the present invention there is provideda resuscitator including a timing valve, a patient outlet and a gasentrainment device, characterised in that the resuscitator includes amanually-displaceable member displaceable to effect simultaneous controlof three separate functions, namely, rate of operation of the tilingvalve, supply of gas to the patient outlet and supply of entrainment gasto the entrainment device.

A resuscitator according to the present invention will now be described,by way of example, with reference to the accompanying drawings, inwhich:

FIG. 1 is a circuit diagram of the resuscitator;

FIG. 2 is a perspective view of the outside of the resuscitator;

FIG. 3 illustrates cam profiles on the manual control button; and

FIG. 4 is a cross-sectional view of the oscillator/timer in greaterdetail.

With reference first to FIGS. 1 and 2 there is shown the variouscomponents of the resuscitator and their interconnections. All thecomponents are contained within a common housing 1, which issufficiently compact and light to be hand held and connected at itspatient outlet 2 directly to a face mask 3. The inlet 4 of theresuscitator is connected via flexible tubing 5 to a source of oxygen,such as a cylinder 6 or, for example, a hospital pipeline, deliveringpressure between 40 and 150 psi. This arrangement enables single-handedoperation, the same hand holding the face mask 3 and controlling theresuscitator. Alternatively, however, the resuscitator could be locatedadjacent the oxygen cylinder and its patient outlet connected to a facemask or breathing tube via flexible tubing.

The inlet 4 is provided by a pressure regulator 10 including a filter 11and an outlet 12, which connects oxygen to various of the othercomponents in the resuscitator. The oxygen splits into five paths. It issupplied to an inlet 13 of an oscillator/timer 14, the inlet 15 of amanual or momentary valve 16, an inlet 17 of a demand detector 18, aninlet 19 of a demand valve 20 and an inlet 21 of a spontaneous breathingvalve 22.

Gas supplied to the oscillator/timer 14 flows to its outlet 23 when theoscillator is open or on and from there passes to an inlet 24 of abi-stable valve 25 the operation of which is controlled by the manualvalve 16. The manual valve 16 and the bi-stable valve 25 can beconsidered together as forming a manual valve assembly. Moreparticularly, operation of the bi-stable valve 25, and hence supply ofgas to the patient, is controlled by gas pressure at its pilot inlet 50,which is connected to the outlet 51 of the manual valve 16.

The manual valve 16 includes a spool 60 movable up and down a verticalbore 61 by the action of either a button 62 or a toggle 63. The inlet 15and outlet 51 open into the bore 61 at locations spaced along its lengthand the spool 60 has seals that can be positioned to permit or preventflow of gas from the inlet 15 to the outlet 51 via the bore. In itsnormal position, as illustrated, a spring 64 urges the button 62, andhence the spool 60, upwards to a position where flow of gas between theinlet 15 and outlet 51 is prevented, so the valve 16 and hence thebi-stable valve 25 is off or closed.

When the button 62 is depressed, the spool 60 moves down and allowspressurised gas at the inlet 15 to pass to the outlet 51 to pilot thepiston 65 of the bi-stable valve 25. Alternatively, any movement of thetoggle 63 beyond a certain angle, will also pull down the spool 60, viaa follower bobbin 66 and crank 67.

When the button 62 or toggle 63 is released, the spool 60 moves upwardlyand pressurised gas piloting the piston 65 escapes to atmosphere via avent 68 at the bottom of the manual valve 16. The manual valve 16 andthe bi-stable valve 25 are arranged so that it is not possible tocontrol the ventilation frequency or flow rate by slight operations ofeither the button 62 or the toggle 63. The output pressure provided bythe bi-stable valve 25 is, therefore, either fully on or fully off.

The outlet 26 of the bi-stable valve 25 connects to a pilot inlet 27 ofa patient dump valve 28, mounted with the spontaneous breathing valve22. While the bi-stable valve 25 is open, that is, during the patientinspiratory phase, pressurised gas exiting at the outlet port 26 pilotsthe patient dump valve 28 at its inlet 27 to cause it to close so thatgas cannot escape via the valve. The outlet 26 of the bi-stable valve 25also connects to two inlets 30 and 31 of a variable restrictor device32, which is manually adjustable to vary both the tidal volume and thefrequency of delivery of gas cycles to the patient.

The restrictor 32 includes a manually-displaceable control member in theform of a rotary plate 70 mechanically coupled with a lever 90 on thecasing 1 so that the plate can be rotated through a limited angle bydisplacing the lever. The restrictor 32 has three tapering grooves oneof which 71 connects the inlet 30 with an outlet 33; the second groove72 connects the inlet 31 with an outlet 37; and the third groove 73connects an inlet 38 with an outlet 39. Rotating the plate 70 relativemovement between the inlets 30, 31 and 38, the outlets 33, 37 and 39 andthe grooves 71 to 73 so as to alter the restriction to flow between therespective inlets and outlets. The first groove 71 controls the timingrate of the oscillator/timer 14. The outlet 33 connects to the controlor timing inlet 34 of the timer 14 so that rotating the plate 70 such asto produce a higher flow of gas to the timer control inlet increases itsfrequency of operation, in a manner described in greater detail later.

Gas supplied to the other inlet 31 of the restrictor 32 flows via thesecond groove 72 to a second outlet 37. The second outlet connects bothto the third inlet 38 of the restrictor 32 and to an inlet 40 of apatient valve assembly 41, via an Air Mix/No Air Mix valve 42. The thirdinlet 38 connects with the third outlet 39 via the third groove 73,which in turn connects to the nozzle inlet 80 of an air entrainmentdevice 81 opening into the patient valve assembly 41.

The second and third grooves 72 and 73 taper in an opposite sense fromthe first groove 71 so that when the plate 70 is rotated to cause anincreased flow at the outlet 33 it causes a reduction in gas flow fromthe other outlets 37 and 39. Thus, if the user moves the lever 90 todemand an increased frequency of ventilation cycles, this rotates theplate 70 and automatically, simultaneously produces a reduced flow rateor tidal volume of gas. A lower operating frequency is used withchildren who also require a lower tidal volume.

Instead of the tapering slots 71 to 73 it would be possible for therestrictor to have rows of holes of increasing sizes.

Operation of the Air Mix/No Air Mix valve 42 connected between theoutlet 33 and the patient valve assembly 41 is controlled by a rotaryknob 142 on the casing 1. The knob 142 can be moved between one of twodifferent positions, marked 100% and 50% respectively. The valve 42controls whether the patient receives pure oxygen (100%), that is, NoAir Mix, or whether this is mixed with air to give an oxygen content ofabout 50%, that is, Air Mix. When the knob 142 is in the 100% position,the valve 42 is filily open and gas from the outlet 37 flowssubstantially entirely directly to the inlet 40 of the patient valveassembly 41 because this route presents a lower resistance to flow. If,however, the knob 142 is turned to the 50% position, it turns the valve42 off completely so that all gas emerging from the outlet 37 now flowsvia the inlet 38, the groove 73 and the outlet 39 to the inlet 80 of theair entrainment device 81. The high velocity jet of oxygen producedwithin the entrainment device 81 draws in air from an air inlet 82,which has an oxygen concentration of about 21%. The resultant gasmixture has a nominal oxygen content of 50% and this enters the patientvalve assembly 41.

The patient valve assembly 41 has the demand valve 20 at its upper endand a patient valve 43 at its lower end opening into the resuscitatoroutlet port 2. The patient valve 43 includes a non-return valve 45 ofconventional kind, such as described in U.S. Pat. No. 4,774,941; Thevalve 43 includes a duck-bill valve, arranged to permit flow of gas fromthe valve assembly 41 to the patient but to prevent flow in the oppositedirection into the interior of the assembly. The valve 45 is supportedcentrally on a flexible diaphragm 46, which bears against the upper endof the outlet port 2. The outlet port 2 is supported coaxially within anouter ring 47 to provide an annular space 48 closed by non-entrainmentflap valves 49. Thus, when the patient exhales, the non-return valve 45closes and the diaphragm 46 lifts off the outlet port 2 to allow theexhaled gas to flow into the annular space 48 and thereby vent toatmosphere via the flap valves 49. The flap valves 49 allow gas to flowout of the annular space 48 but prevent flow in the opposite direction.

Operation of the oscillator/timer 14 will now be described in moredetail with reference to FIG. 4. The oscillator/timer 14 has an outertubular housing 140 into which the control inlet 34 and outlet 23 openaxially. The outlet 23 opens into the left-hand end of a relativelysmall diameter axial bore or passage 141, which opens at its right-handend into a larger diameter cavity 142. The inlet 13 of theoscillator/timer 14 opens laterally into the bore 141 about midway alongits length. Inside the bore 141 there are two O-ring seals 143 and 144,one being located between the inlet 13 and the outlet 23 and the otherbeing located between the inlet 13 and the opening of the bore into thecavity 142. Within the cavity 142 are mounted a sealing rod 145, a capor piston 146, two helical springs 147 and 148 and a diaphragm 149. Thesealing rod 145 is mounted axially and extends with its left-hand end150 located in the bore 141 and its right-hand end 151 retained withinthe cap 146. The left-hand end 150 of the rod 145 has an enlargedannular bead 152 set back a short distance from its end and positionedbetween the two O-rings 143 and 144. The rod 145 extends through theright-hand O-ring 144, which makes a sliding, sealing engagement withthe outside of the rod. The right-hand end of the rod 145 has anenlarged flange 153 spaced a short distance from its end, which isengaged on its right-hand side by the left-hand end of the spring 147.The spring 147 extends axially and abuts the inside, closed, right-handend 246 of the cap 146. The left-hand side of the flange 153 abuts theright-hand side of a flange 154 projecting inwardly of the cap 146 aboutmidway along its length. The left-hand end 155 of the cap 146 is openand enlarged to form an internal shoulder 156 and it is a loose,non-sealing, sliding fit within the cavity 142. The shoulder 156 iscontacted by the right-hand end of the second helical spring 148, whichis of larger diameter than the first spring 147 and extends axiallyaround the sealing rod 145. The left-hand end of the second spring 148abuts an end wall 157 at the left-hand end of the cavity 142.

The oscillator/timer 14 is completed by the diaphragm 149, which is madeof a flexible, impervious, low stiffness fabric and silicone rubbermaterial. The diaphragm 149 is circular in shape with a thickenedcircumferential lip 158, which is trapped and sealed between two partsof the housing 1 such that the diaphragm extends transversely of thecavity 142 and seals a rear part 159 of the cavity from a forward part160. The central part of the diaphragm 149 is moulded with a mesaformation 161 projecting into the rear part 159 of the cavity 142 andclosely embracing the external surface of the rear, closed end of thecap 146. Between the mesa formation 161 and the lip 158 the diaphragm149 curves forwardly around a curved annular lip 162 on the inside ofthe housing 140 and is formed into a U-shape rolling loop 163 in theannular space 164 between the inside of the housing and the outside ofthe rear part 246 of the cap 146.

In the natural position of the oscillator/timer 14, the spring 148pushes the cap 146, and hence the sealing rod 145, rearwardly to aposition where the annular bead 152 on the rod is rearwardly, that is,to the right of the opening of the inlet 13 into the bore 141. Thepassage between the inlet 13 and the outlet 23 is, therefore,unobstructed so that gas can flow through the oscillator/timer 14 and itis on or open. Movement of the sealing rod 145, therefore controls flowof gas along a passage through the oscillator/timer between the inlet 13and the outlet 23.

When gas pressure is supplied to the control inlet 34, pressure withinthe rear part 159 of the cavity 142 increases. This causes pressure tobe applied to the right-hand side of the diaphragm 149 forcing itagainst the cap 146 and moving the cap forwardly like a piston, to theleft against the action of the spring 148. Air within the left-hand partof the cavity 142 can escape to atmosphere through a small vent hole 165in the housing 140. As the cap 146 moves to the left, the diaphragm 149flexes and the loop 163 rolls between the cap and the housing 140,peeling off the outside of the cap and folding against the inside of thehousing. Pressure in the bore 141 initially prevents the rod 145 movingso that the spring 147 is compressed as the piston moves forwards. Whenthe rear end 151 of the rod 145 bottoms on the rear end 246 of thepiston, the rod is moved forwardly along the bore 141moves until itsrear end The spring 147 within the cap 146 bears against the flange 153on the sealing rod 145 to keep it in contact with the flange 154 on thecap, thereby moving the sealing rod forwardly, along the bore 141. Asthe rod 145 moves forwardly its annular bead 152 moves to the left ofthe inlet 13 and the forward end 150 of the rod starts to enter theforward O-ring 143. Pressure across the bead 152 is now equalized andthe force of the spring 147 is sufficient to push the rod forwardly sothat its bead is in full sealing contact with the left-hand O-ring 143.It can be seen that this blocks flow of gas from the inlet 13 to theoutlet 23 and thereby turns the oscillator/timer 14 off. This terminatesthe inspiratory phase of gas delivery to the patient and starts theexpiratory phase.

When the timer/oscillator 14 turns off, all gas in the charging circuitbetween the outlet 23 of the timer 14 and the inlet 30 of the restrictor32 escapes to atmosphere through -the patient valve assembly 41, eitherdirectly via the inlet 40 or via the entrainment device 81. Thisreleases pressure on the patient dump valve 28, allowing it to open,which, in turn, allows the patient circuit pressure to quickly vent toatmosphere via ports in the patient dump valve.

When pressure at the control inlet 34 falls, the spring 148 starts tomove the sealing rod 145 back to the open position. Gas in the rear part159 of the cavity 142 escapes via the inlet 34 back to the restrictor 32and, in particular, flows to the inlet 30 via the groove 71. The rate ofdecay of gas pressure is, therefore, determined by the timer setting ofthe restrictor 32. Once the oscillator/timer 14 is open again a newinspiratory phase starts and the ventilation cycles continue.

It can be seen that the diaphragm 149 provides a complete seal betweenthe two parts 159 and 160 of the cavity 142 and does not rely on moving,wiping seals or this like. Conventional pneumatic pistons use an O-ringto produce a seal. The present construction enables the timing valve 14to operate with lower friction and stiction forces and hence enables thevalve to operate reliably at lower switching pressures. It is importantto keep the switching pressures as low as possible in order to ensurethat the tidal volume of the first inspiratory breath delivered is notunduly increased. When the manual button 62 is first actuated, thetiming valve 14 is open so gas can flow to the patient until pressure atthe control inlet 34 has risen to the closing switching pressure. Ifthis pressure were relatively high, gas would flow to the patient for alonger time and the tidal volume delivered could be unduly high. Iflower switching pressures are used in conventional, O-ring valves, thereis a higher risk of failure especially at very low temperatures of downto −18° C. and especially if the valve is of a small size. Thearrangement described can have low friction and stiction forces in asmall oscillator over a wide range of temperatures between −18° C. and+50° C.

When using the manual control button 62 or toggle 63, the inspiratoryperiod of the resuscitator lasts for as long as the button is depressedor the toggle is deflected, up to the point of a maximum inspiratorytime, as determined by the oscillator/timer 14 and the setting of thevariable restrictor 32. With this method of operation it is possible todeliver any volume less than the full tidal volume by releasing thebutton or lever before complete delivery. By cutting the delivery short,another inspiratory cycle can be delivered proportional to theincomplete volume not delivered and to the time elapsed (the expiratorytime) before button 62 is next pressed or the toggle 63 is deflected. Itis not possible to deliver two or more full breaths in very closesuccession, thereby avoiding the possibility of creating stacked breathsand over inflating the patient. If a full 100% tidal volume isdelivered, the circuit will lockout until the full expiratory time haspassed. After which time, another inspiratory time can be deliveredunder control.

The automatic cycle mode is achieved by holding down the spool 60 bysome releasable, mechanical means. In the present example, this isachieved by a rotatable ring 262 surrounding the button 62. When thering 262 is rotated to its “Automatic” position, two cam pins 263projecting radially inwardly of the ring engage an inclined portion 264of two cam profiles 265 (as shown in FIG. 3) formed diametricallyopposite one another on the outside of the button 62, thereby pushingdown the button. In this way, the button 62 is held in the actuatedposition and the resuscitator delivers repeated timed ventilation cyclesone after the other at a frequency and tidal volume determined byoperation of the oscillator/timer 14 and the setting of the restrictor32. When the ring 262 is rotated back to its “Manual” setting, the campins 263 align with vertical sections 266 of the cam profiles 265 sothat movement of the button 62 is not impeded.

During any phase of the ventilation cycle, if the patient takes a demandbreath, a demand flow will be provided by the demand valve 20. If thedemand breath exceeds a pre-set tidal volume and frequency combination,the automatic cycling, if being used, will be temporarily inhibited.During this operation the pressure in the patient circuit drops a fewmbar below atmospheric pressure, drawing down a diaphragm 170 in thedemand valve 20. Pressure already supplied to the demand valve 20 at theinlet port 19 will have equalized above and below a flexible seal 171and will have piloted one side of the demand detector 18 via a port 172.Movement of the diaphragm 170 acts on a valve lever 173 and allowspressure above the seal 171 to flow out from a port 174. This actioncreates a pressure drop across seal 171, which allows gas, at a flowrate demanded by the patient, to enter the patient-circuit.Simultaneously, the drop in pressure above the seal 171 allows adiaphragm 175 of the demand detector 18 to move to the left and opens apath for gas through the demand detector 18 from the inlet 17 to theoutlet 176. The gas then passes through a non-return valve 177 topressurize the timer/oscillator circuit at its control inlet 34. Thispressurisation moves the cap 146 and the sealing rod 145 until the pathof gas between the inlet 13 and 23 stops, thus, temporarily inhibitingthe automatic cycling. When the patient's demand breath has finished,pressure above and below the seal 171 equalizes again and the diaphragm175 of the demand detector 18 returns back, stopping the path of gas tothe outlet 176. At this stage, gas trapped in the oscillator circuitescapes via the normal route and the automatic cycle, in time, willrecommence, if in this mode, unless another demand breath is taken. Thelevel of the demand breath dictates the time allowed to charge theoscillator circuit and thus the expiration time available.

In order to limit the maximum patient circuit pressure, the resuscitatorfurther incorporates a pressure relief valve 180 connected to theinterior of the patient valve assembly 41. This opens to atmosphere torelieve excess flow when a pre-determined pressure is exceeded.

The spontaneous breathing valve 22 includes a piston 181 acted on by aspring 182 to move it to a position where the valve is open to air. Thepiston 181 is also acted on by gas supply pressure from the regulator 10such that it is normally held closed. However, if the supply pressureshould drop, the valve 22 will open to enable a spontaneously breathingpatient to breathe to atmosphere. This provides an alternative breathingpath if the supply gas pressure should fall below the input pressurerequirements of the demand valve 20.

The circuit may include adjustable restrictors at locations A and B inFIG. 1 by which operation of the resuscitator can be tuned. Inparticular, a restrictor at position A, between the inlet 172 of thedemand detector 18 and the demand valve 20, would be used to control theresponse of the diaphragm 175 in the demand detector. The otherrestrictor at position B, between the outlet 176 of the demand detector18 and the inlet 34 of the timer/oscillator 14, would be used to controlthe rate at which the timer/oscillator is filled when a patient demandbreath has triggered the demand detector.

1. A resuscitator operable in a first, automatic mode whereby gas isdelivered to a patient in a regulated cyclical fashion repeatedly untilthe mode is terminated and in a second mode whereby a cycle of gas isdelivered in response to actuation of a manual member, characterized inthat the resuscitator is arranged such that the cycle is only deliveredfor so long as the manual member is actuated and that the resuscitatorcontrols the maximum length of the cycle.
 2. A resuscitator according toclaim 1, characterized in that the resuscitator is arranged to deliverrepeated ventilation cycles while the manual member is actuated.
 3. Aresuscitator according to claim 2, characterized in that theresuscitator includes a locking device for holding the manual member inan actuated position.
 4. A resuscitator according to claim 3,characterized in that the manual member includes a button that isdepressed to actuate a gas delivery cycle, and that the locking deviceincludes a rotatable member operable to retain the button in an actuatedposition.
 5. A resuscitator according to claim 4, characterized in thatthe rotatable member extends around the button and is arranged todepress the button when rotated.
 6. A resuscitator according to claim 5,characterized in that rotatable member and the button have cooperatingcam formations.
 7. A resuscitator according to claim 1 characterized inthat resuscitator includes a first valve controlled by operation of themanual member and a bi-stable valve connected with the first valve to beoperated between a fully open or a fully closed position by an outputfrom the first valve, and that the bi-stable valve controls supply ofgas to the outlet of the resuscitator.
 8. A resuscitator according toclaim 1 characterized in that the resuscitator includes a timing valveoperable to supply cycles of ventilation gas to a patient valveassembly, that the output of the timing valve is connected to a manualvalve assembly operable by the manual member to prevent or enable flowof ventilation gas to the patient valve assembly, and that the output ofthe manual valve assembly is connected to a control inlet of the timingvalve.
 9. A resuscitator according to claim 1 characterized in that theresuscitator includes a manually-displaceable control member that isdisplaceable to alter timing frequency and flow rate simultaneously. 10.A resuscitator according to claim 9, characterized in that theresuscitator includes a gas entrainment device and that themanually-displaceable control member is operable also simultaneously tocontrol the supply of entrainment gas to the entrainment device.
 11. Aresuscitator according to claim 9, characterized in that themanually-displaceable control member includes a rotatable member.
 12. Aresuscitator including a timing valve operable to supply cycles ofventilation gas to a patient assembly, characterized in that the outputof the timing valve is connected to a manual valve assembly, which isoperable to prevent or enable flow of ventilation gas to the patientvalve assembly, and that the outlet of the manual valve assembly isconnected to a control inlet of the timing valve.
 13. A resuscitatorincluding a timing valve, a patient outlet and a gas entrainment device,characterized in that the resuscitator includes a manually-displaceablemember displaceable to effect simultaneous control of three separatefunctions, namely, rate of operation of the timing valve, supply of gasto the patient outlet and supply of entrainment gas to the entrainmentdevice.